N = int(input())
txt  = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'

c = [0]*9
nxt = N
for rank in range(0,10):
	if N/(26**(rank+1)) <= 1:
		break
targ = N
for i in range(rank,-1,-1):
	p = targ/(26**i)
	c[i] = p-1 if i !=0 else p
	targ -= p*(26**i)
	
print "".join([txt[c[j]] for j in range(rank,-1,-1)])